1. Field of the Invention
This invention relates to apparatus and method for rimming or curling, and more particularly to a tooled die mechanism which is employed to form the rim of open mouth containers. The present invention is particularly adapted to forming a helicoidal rim at the mouth of drinking cups and other types of frustoconically-shaped containers where the rim must be durably and uniformly fabricated.
2. Description of the Prior Art
Previously, many types of paper and thermoplastic containers have been rimmed by spinning tool crimpers and externally heated non-rotating means. Both methods essentially form a rim by pushing against the unsupported leading edge of the frustoconically-shaped container. This frequently results in collapse of the unsupported sidewall area and/or nonuniformly formed rims. In addition, the spinning tool types of crimpers introduce a torque to the unsupported leading edge of the frustoconically-shaped container. This torque plus axial force causes a twisting type of collapse to the container wall in addition to the previously described failure due to axial motion only. These aforementioned distortions or wrinkles disastrously affect the overall strength and appearance of the container.
Various types of rimming tool methods have not heretofore been capable of providing structural support to the portion of the container blank to be rimmed during the actual formulation of the rim. This lack of support to the length of the blank to be rimmed plus the lack of support adjacent the rim results in loss of production or making containers having sidewall variations or wrinkling thereat which affect the overall appearance and performance of the containers. Obviously rim strength and its uniform adjacent sidewall are important characteristics in the manufacture of relatively thin-walled cups of various sizes, whether they be fabricated of paper, thermoplastic, or other materials. When the sidewall adjacent the open edge is unsupported during rimming, it is not uncommon for the sidewall to be wrinkled or misshapened during rimming which produces containers lacking in high-quality performance and appearance.
The present invention provides an improved mandrel mechanism and method for rimming container bodies and especially paper and plastic cups which may be radially curled while maintaining the sidewalls in fully supported arrangement. The improved mandrel and stationary rimming tool mechanism of the present invention facilitate rimming paper and plastic containers at relatively high speeds in an efficient manner, such that the deleterious effects of container sidewall warping and distortion are eliminated. The present apparatus and method provide means for forming more uniform and strongly reinforced rims at the mouth of containers having generally cylindrical or tapered sidewalls, the rim being formed with a helicoidal configuration adapted to the engagement with a container closure for durable sealing. While the invention is primarily directed to radially curling containers of an essentially circular cross-sectional configuration, the apparatus permits forming either helicoidal or elongated rims with essentially uniform adjacent sidewalls from which the rims depend.
U.S. Pat. No. 2,778,287 to Moore relates to apparatus for curling containers without requiring any spinning or rotational movement. The curling die forming the curled rim is actuated longitudinally coincident with the axis of the body wall of the container; however, such apparatus is not capable of rimming conically-shaped containers with the uniformity and strength required of modern day containers when made by high speed production methods.
These and other objects of the present invention will become more fully apparent with reference to the following specification and drawings which relate to the preferred embodiment thereof for the manufacture of paper, thermoplastic, or other containers.